Insulin-like growth factors and fish reproduction

Abstract

Knowledge on fish reproduction is of high relevance for basic fish biology and comparative evolution. Furthermore, fish represent excellent biomedical models and the impact of aquaculture in world-wide food production is steadily increasing. Consequently, research on reproduction of fishes and the potential modes of its manipulation get more and more important. Reproduction in fishes is regulated by the integration of endogenous neuroendocrine (gonadotropins), endocrine and autocrine/paracrine signals with exogenous (environmental) factors. The main endocrine regulators of gonadal sex differentiation and function are steroid hormones. However, recent studies suggest that other hormones are also involved. Most prominent among these factors are the insulin-like growth factors (Igfs), i.e. Igf1, Igf2, and most recently Igf3. Thus, the present review deals with the expression patterns and potential physiological functions of Igf1 and Igf2 in male and female gonads. It further considers the potential involvement of growth hormone (Gh) and balances the reasons for endocrine vs. auto/paracrine actions of the Igfs on the gonads of fishes. Finally, the review discusses the early and late development of gonadal Igf1 and Igf2 and whether they are targets of endocrine disrupting compounds. Future topics for novel research investigations on Igfs and fish reproduction are presented.

Abstract

Knowledge on fish reproduction is of high relevance for basic fish biology and comparative evolution. Furthermore, fish represent excellent biomedical models and the impact of aquaculture in world-wide food production is steadily increasing. Consequently, research on reproduction of fishes and the potential modes of its manipulation get more and more important. Reproduction in fishes is regulated by the integration of endogenous neuroendocrine (gonadotropins), endocrine and autocrine/paracrine signals with exogenous (environmental) factors. The main endocrine regulators of gonadal sex differentiation and function are steroid hormones. However, recent studies suggest that other hormones are also involved. Most prominent among these factors are the insulin-like growth factors (Igfs), i.e. Igf1, Igf2, and most recently Igf3. Thus, the present review deals with the expression patterns and potential physiological functions of Igf1 and Igf2 in male and female gonads. It further considers the potential involvement of growth hormone (Gh) and balances the reasons for endocrine vs. auto/paracrine actions of the Igfs on the gonads of fishes. Finally, the review discusses the early and late development of gonadal Igf1 and Igf2 and whether they are targets of endocrine disrupting compounds. Future topics for novel research investigations on Igfs and fish reproduction are presented.

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